Problem with my SB-900 need help!

[kkcharles82]

I believe you've got the idea of AutoFP wrong. It does consume more power as the flash has to be on at a longer flash duration at the same power to compensate for a narrower travelling shutter "slit". That's why the guide number drops, because part of the flash output is blocked out by the travelling shutter. At the normal flash-sync speed, the full flash output is captured by the CCD as the focal plane is fully opened ... that's why the guide number is higher. So for any given situation, AutoFP will alway fire at a higher power compared to non-AutoFP mode and hence require more time to dissipate the heat.

I think you can refer to this link http://www.planetneil.com/tangents/2008/12/13/max-it-out/ and see if it makes sense to you. Do you have any references to the comments so that we can refer to and see if the references have contradicting conclusions?

Quote from the website "So with the older flash technology, flash is dissipated as that high-energy burst of light .. but camera manufacturers came up with the stunning adaptation of that technology, where they dissipate the energy from the flash as rapidly pulsed light. In effect, the flash now becomes continuous light over a very short period. The light from the flash is now dissipated even as the shutter curtains move across the frame. As that window between the two curtains move across the frame, the light from the camera’s speedlight is dissipated … exposing correctly for the entire frame. Remarkable technology!"

Take 1/50 as the minimum shutter speed where there is a period of time when the entire shutter is open, if we speeded up the shot to 1/100, you will land up with a moving slit the size of HALF of shutter but still moving across the entire scene in 1/50 second. So for BOTH the situations, the flash duration needs to stay the same, but for the latter, the flash output must remain relatively constant or else parts of the sensor will be exposed to varying degree. AutoFP ensure that the flash output remains constant throughout not by increasing the power output and draining the capacitor, but extends the flash duration such that the illumination remains constant throughout the frame.

 

[linse]

I think you can refer to this link http://www.planetneil.com/tangents/2008/12/13/max-it-out/ and see if it makes sense to you. Do you have any references to the comments so that we can refer to and see if the references have contradicting conclusions?

I'm afraid I can't quote any references of the top of my head as I read up all flash technologies from hardcopy photography books years ago.

Quote from the website "So with the older flash technology, flash is dissipated as that high-energy burst of light .. but camera manufacturers came up with the stunning adaptation of that technology, where they dissipate the energy from the flash as rapidly pulsed light. In effect, the flash now becomes continuous light over a very short period. The light from the flash is now dissipated even as the shutter curtains move across the frame. As that window between the two curtains move across the frame, the light from the camera’s speedlight is dissipated … exposing correctly for the entire frame. Remarkable technology!"

I agree with this completely. I don't think I have contradicted this statement.

Take 1/50 as the minimum shutter speed where there is a period of time when the entire shutter is open, if we speeded up the shot to 1/100, you will land up with a moving slit the size of HALF of shutter but still moving across the entire scene in 1/50 second. So for BOTH the situations, the flash duration needs to stay the same, but for the latter, the flash output must remain relatively constant or else parts of the sensor will be exposed to varying degree. AutoFP ensure that the flash output remains constant throughout not by increasing the power output and draining the capacitor, but extends the flash duration such that the illumination remains constant throughout the frame.

I believe this assumption is wrong. The flash duration is obviously not the same. Neither is the total flash output. Taking maximum flash-sync shutter speed as 1/50, at double to max flash-sync speed (1/100s), half the CCD/CMOS will be blocked by the shutter. If the power output is the same, at 1/100s the CCD/CMOS exposure will be exactly halved. So to compensate, the total flash output has to be doubled. As a result, At 1/100s, the guide number drops by half. There is no other reason why the guide number drops when using Auto-FP mode. So, because the flash runs at higher total output levels with AutoFP, it gets hotter and uses more battery.

 

[jopel]

Tks to all respond,i just came back from NSC.
got one very simple solution just need to deactivate the themal funtion,problem solve.
control the flash usage just need to be gentle abit for this one:bsmilie:

This is not a solution at all. If that is the solution nikon should not have this thermal function in the SB900 at all.

Try use only alkaline battery. Rechargeable battery, especially those that have been recharged numerous times, will get hot fast hence triggering the thermal warning.

 

[zac08]

This is not a solution at all. If that is the solution nikon should not have this thermal function in the SB900 at all.

Try use only alkaline battery. Rechargeable battery, especially those that have been recharged numerous times, will get hot fast hence triggering the thermal warning.

Isn't the thermal warning for the flash tube instead of the battery compartment?? :think:

 

[linse]

Isn't the thermal warning for the flash tube instead of the battery compartment?? :think:

I agree. The only reason the flash tube does not get as hot with alkali batteries is because of the slower cycling time of alkali batteries (and hence longer time to cool down the flash tube between flashes) compared to rechargeable batteries.

 

[jopel]

Isn't the thermal warning for the flash tube instead of the battery compartment?? :think:

It is just a irritating and fustrating flase alarm, hence, NSC told TS to turn it off.

btw alkaline reycle faster than rechargeable battery. Try it on the continous mode you will see the different.

 

[blazer_workz]

It is just a irritating and fustrating flase alarm, hence, NSC told TS to turn it off.

btw alkaline reycle faster than rechargeable battery. Try it on the continous mode you will see the different.

Just wondering..if tube really blown due to thermal overheat..who will bear the cost? we or nsc?

 

[jopel]

Just wondering..if tube really blown due to thermal overheat..who will bear the cost? we or nsc?

try yours and let us know :bsmilie:

 

[linse]

btw alkaline reycle faster than rechargeable battery. Try it on the continous mode you will see the different.

NiMH and NiCd batteries have lower internal resistance than alkali batteries. That is why they recycle faster than alkali for high drain devices like flashes.

If you look at this link, [FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1]recycle time to full power for [/SIZE][/FONT]alkali batteries [FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1]can range from 6-20 seconds, depending on how new the cells are. [/SIZE][/FONT][FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1]NiMH have a similar recycle time as NiCads - around 4-6 seconds. [/SIZE][/FONT]